It is believed that, in the transition from hepatitis/liver cirrhosis into liver cancer, the amount of α-fetoprotein (AFP) binding to Lens culinaris agglutinin (LCA) (i.e., LCA-binding AFP) in a biological sample increases. JP S63-307900 describes an antibody for detecting LCA-binding AFP. In JP S63-307900, it is described that an antibody disclosed in this document is reactive with LCA-binding AFP but is unreactive with LCA non-binding AFP.
In JP S63-307900, it is described that LCA-binding AFP contains fucose in the sugar chain moiety thereof. A fraction of AFP binding to Lens culinaris agglutinin in a biological sample is called an “AFP-L3 fraction”. The AFP-L3 fraction is composed of fucosylated AFP (i.e., AFP having a structure such that core fucose (i.e., fucose bonding to N-acetylglucosamine (GlcNAc), which is located at a reducing terminal of an N-type sugar chain via an α1-6 bond) is added to an asparagine residue in the AFP).
In the section “Examples” in JP S63-307900, an antibody which binds to LCA-binding AFP (AFP-LCA-R) but does not bind to LCA non-binding AFP (AFP-LCA-NR) is produced (see Example 1, FIGS. 1 and 5). However, an epitope for the antibody is unknown. In the section “Examples”, it is concluded that the bindability or non-bindability of the antibody to LCA depends on the presence or absence of fucose, as mentioned above. Therefore, there is a possibility that the bindability of the antibody to an antigen depends on the presence of a fucose moiety in the antigen rather than the sequence for a peptide moiety in the antigen. In this case, the antibody may bind to other fucose-containing proteins non-specifically, as well as AFP. For these reasons, the development of a monoclonal antibody for which the epitopes in a glycopeptide are both of a fucose moiety in the glycopeptide and an amino acid residue contained in a peptide moiety in the glycopeptide has been demanded.